Windows and doors are typically mounted in frames that include a sill at the bottom of the opening in which the window or door is located. It is desirable to limit the passage of water through the window or door when it is closed. That goal is, however, often complicated by a competing interest in providing a sill that has minimal impact on passageway through the opening in which the window or door is located. In particular, in many situations it may be desirable to provide a sill that presents a low profile to allow the passageway of wheeled traffic such as, e.g., wheelchairs, carts, etc.